Preparation of elastic polychloroprene threads, bands, etc.



Patented Sept. 27, 1949 PREPARATION OF ELASTIC POLYCHLORO- PRENE THREADS, BANDS, ETC.

Robert Henry Walsh, Woodstown, N. J., assignor to E. I. du Pont de Nemours & Company,

Wil-

mington, Del., a corporation of Delaware No Drawing. Application January 4, 1947, Serial No. 720,314

This invention relates to the production of polychloroprene latices, particularly suitable for the preparation of elastic threads, sheets and bands and other structures which are subject to stretching at elevated temperatures.

Thread produced from polychloroprenelatex, while exhibiting excellent tensile strength, elongation, modulus and permanent set characteristics at normal temperatures, does not retain all of these good properties when tested at temperatures exceeding 200 F. Thus, when subjected to a strain of 200% at the temperature of boiling water, polychloroprene thread will rupture unless properly compounded. In the preparation of webbing and knitted elastic fabrics where the process often requires immersion of the material at 200% elongation in boiling water, such conditions result in broken threads and, therefore, loss in fabric strength and elasticity. Even when this treatment is not severe enough to cause breakage of the thread, a permanent and undesirable distortion of the thread is generally observed.

Again, in the manufacture of golf balls, where the thread is Wound on a core under tension, the cover then applied, and the ball cured at high temperatures, thermal strain causes the thread to break with resulting loss in resiliency of the finished article.

An object of the present invention is therefore to improve the resistance of polychloroprene thread and similar structures to breakage when subjected to prolonged stretching at elevated temperatures. A further object is to reduce the permanent set produced under such conditions.

I have found that these objects are accomplished by incorporating into the polychloroprene latex prior to coagulating and curing a small amount of a sulfurized monocyclic terpene hydrocarbon.

The improvement caused by a typical sulfurized terpene, when added to a compounded latex designed for the production of thread, is illustrated in the following examples.

2 Claims. 26029.7)

Parts Polychloroprene 100.0 Zinc oxide 5.0 Phenyl beta-naphthylamine 2.0 A12O3.3H2O (alorco 0340) 10.0 Sulfated methyl oleate (aquarex SMO) 1.5 Naphthenic acids and oils (sunaptic acid) 1.0

The zinc oxide (curing agent), aluminum chloride (filler known to increase heat resistance) and phenyl beta-naphthylamine (antioxidant) were dispersed by grinding in aqueous solutions of ammoniacal casein and the sodium salts of sulfonated dinaphthylmethane obtained from naphthalene, sulfuric acid and formaldehyde before adding them to the latex. The sulfated methyl oleate (sodium salts) and naphthenic acids, which were used to reduce surface irregularities in the finished dry products, were dissolved in ,water and dilute ammonium hydroxide, respectively, and added to the latex,

The sulfurized terpene used in the following examples was made according to the process of U. S. Patent 2,443,823 of Holt which issued June 22, 1948, by treating with'sulfur at to C. the mixture of hydrocarbons obtained as a by-product in the isomerization of pinene to camphene and containing dipentene and terpinoline as the active ingredients, From about 1.5 to about 2.1 atoms of sulfur for each .mol of unsaturated terpene are employed and the heating is continued until a substantial portion of the terpene is sulfurized. The crude sulfurization mass was then washed with aqueous sodium sulfide solution to remove free sulfur and topped to remove the unreacted hydrocarbons, according to the further teachings of the Holt application. The resulting refined sulfurized product containing from 24% to 36% of combined sulfur was put into a form particularly suitable for addition to the latex by mixing 100 parts of the product with one part of oleic acid, dispersing this mixture with high-speed agitation in 10 parts of 10% potassium hydroxide solution and 50 parts of 10% ammoniacal casein solution, and diluting the resulting dispersion with 41 parts of water.

This emulsion was added to the polychloroprene latex compound described above in amounts furnishing the parts by weight of sulrurized product per 100 parts of dry polychloro- Modulus (800%) prene given in the following table. Films were .made from these compositions by the so-called anode process, as more particularly described in U. 5. Patents 1,908,719, 1,959,021 and 1,996,051. The finished films were washed in water at 70 C., dried and vulcanized by heating at 140 C. for 60 minutes. The following test, developed by users of elastic thread, was used to evaluate the behavior of the polychloroprene formulations at elevated temperatures. Flat dumbbell-shaped test pieces were cut from the test film, placed in a rack and elongated 200%. The rack was then immersed in boiling water. The time required for the sample to break was noted. If the sample did not break at the end of one hour, it was assumed that the thread would not rupture at all at this temperature. I The samples were removed from the water bath, relaxed and the permanent set measured after minutes. The average value of three tests is reported. The lower the permanent set, the more resistant is the film to thermal shock. This data is included in. the following table, along with moduli for 800% elongation at room temperature, which shows the effect of the sulfurized terpene upon the curing characteristics. Example 1, in which no sulfurized terpene was used, was included for comparison but is not an embodiment of the present invention.

4 furized terpene) gave an elongation of only 200%, while those containing 2% of sulfurized terpene (Example 3) gave an elongation of 500%.

It is interesting to note that neither free sulfur nor the unsulfurized terpene, individually nor combined, have any of the favorable effects upon the properties of the polychloroprene at high temperatures such as are shown by their reaction product, namely, the sulfurized terpene.

It is obvious that considerable variations may be made from the above specific examples in carrying out this invention. Thus, any rubberlike polymer of chloroprene may be used. Any of the usual pigments, fillers, vulcanizing agents, antioxidants may be used. Although the preferred agent is made from a mixture of dipentene and terpinolene as described above, either of these terpenes may be sulfurized alone, or other unsaturated monocyclic terpene hydrocarbons may be used. Furthermore, the purification of the sulfurized terpene to remove free unreacted sulfur 'and hydrocarbons may be omitted. The sulfurized terpene may be dispersed directly in the latex without first forming a highly stable suspension thereof.

Latex containing the sulfurized terpene may be used for the production of elastic thread by any of the methods used for the purpose. It may also be used to advantage in making sheets,

Example Parts of sulfurized terpene per 100 parts of polychloroprene Breaking time, min Permanent set, percent er 60 minutes) (not broken at It will be seen from this that 1% or more of the sulfurized terpene prevents thermal breakingin the standard test and that about 2% gives the minimum permanent set under these conditions. When more than 4% (based on thepolychloroprene) of sulfurized terpene is added to the formulation, the rate of cure is retarded, as

shown by the lower modulus at 800% elongation.

For some purposes such retardation is undesirable and the preferred amount of sulfurized terpene is between 1% and 4%, although higher amounts may sometimes be used to advantage. The most preferred amount is 2%.

Still another method of measuring the resistance of latex thread to thermal breakage has been proposed by thread manufacturers. In this test, threads or dumbbells from the test films are placed in a rack and different samples are elongated equivalent to 200%, 250%, 300% and 350% elongation, respectively, and then placed in boiling water. If at the end of 5 minutes none of the samples have broken, the rack is reloaded with new samples and elongated to 400%, 450%, 500%. The rack is again immersed in boiling water for 5 minutes. This procedure is repeated until the samples break. The breaking elongation is reported. The higher the elongation, the greater is the resistance of the stock to thermal breakage. This test was applied to films from polychloroprene latex, compounded as in Examples 1 and 3. Films compounded as in Example 1 (containing no sulbands, and other structures which are subject to stretching at elevated temperatures.

I claim:

1. A polychloroprene latex particularly adapted for use in the preparation of elastic polychloroprene thread, bands and sheets, having incorporated therein from 1% to 4%, based on the polychloroprene present in the latex, of a sulfurized monocyclic terpene hydrocarbon containing from 24% to 36% of combined sulfur.

2. A polychloroprene latex particularly adapt-- ed for use in the preparation of elastic polychloroprene thread, bands and sheets, having incorporated therein from 1% to 4%, based on the polychloroprene present in the latex, of a sulfurized mixture of hydrocarbons obtained as a by-product in the isomerization of pinene to camphene and containing dipentene and terpinolene as the active ingredients, which mixture contains from 24% to 36% of combined sulfur.

ROBERT HENRY WALSH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,046,499 Calise July 7, 1936 FOREIGN PATENTS Number Country Date 452,078 Great Britain Aug. 17, 1936 

